Refactor nova with pyupgrade to remove legacy python syntax

This proposal simply apply automated refactoring to nova using pyupgrade to remove legacy python 2 and <3.8 syntax.

pyupgrade (https://github.com/asottile/pyupgrade) is a tool (and pre-commit hook) to automatically upgrade syntax for newer versions of the language. In the context of nova this primarily means the removal of legacy py2.7 code such as % strings formating which is now blocked by hacking in favor of f'strings' , removal of explicit unicode strings (all strings are unicode by default since py3.0, explciy new style classes (myclass(object): and other syntax not required based on our min python version.

our current pytyon min version support is 3.8 and this proposal does not change that.